Substantial position correction to the Andvord Bay coastline and ...
This association of grain size and magnetic susceptibility intensity in the core scanning data can yield important preliminary evidence concerning the size and composition of antarctic glacial-marine sediment. For example, peaks in the magnetic susceptibility record of piston core 71 (which can be quickly generated from long piston core samples and processed on board the research vessel, see figure 3B) should represent strata of higher sand and heavy mineral content which may also prove to be more well sorted. Intermediate strength magnetic susceptibility peaks should be indicative of a more poorly sorted, icerafted, deposit. The sediment commonly having the least amount of magnetized material is the distant diatomaceous ooze deposit located at distances exceeding 10 nautical miles from the glacial ice front. Given the surface depositional pattern of Eolian sediment, one can infer the recent sedimentary history of Lallemand. The down-core magnetic susceptibility read ings can be interpreted relative to the advance and retreat of the present shelf ice front. Higher magnetic susceptibility values would result from a proximal ice front, and lower values would occur if the ice shelf either extended over the sampling site or receded to a distance in excess of some 10 nautical miles from the site. The ease and utility of the core scanning mag-
Substantial position correction to the Andvord Bay coastline and bathymetry using global positioning system and radar imaging
netic-susceptibility-sensor process when combined with the depositional patterns provide a powerful tool for antarctic paleoclimatic analysis. This preliminary study was supported by National Science Foundation grant DPP 89-15977 to Eugene W. Domack and Charles E. McClennen.
References Andrews, J.T., and A.E. Jennings. 1987 Influence of sediment source and type on the magnetic susceptibility of fjord and shelf deposits, Baffin Island and Baffin Bay, N.W.T. Canadian Journal of Earth Sciences, 24, 1386-1401. Barrett, P.J., A.R. Pyre, and B.L Ward. 1983. Modern sedimentation in McMurdo Sound, Antarctica. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic earth science. Canberra: Australian Academy of Science, Canberra. Domack, E.W., L.A. Burkley, and C.R. Williams. 1989. Character of modern glacial marine sediments: Antarctic Peninsula and South Shetland Islands. Antarctic Journal of the U.S., 24(5), 113-115. Harris, J. S., and E. A. Fleming. 1979. Geologic Map Series BAS500G, Sheet 3, Edition 1. Loubet Coast: British Antarctic Survey.
larged over 10 times, using a Savin 7220 copier, was similar in outline to the projection of a 35-millimeter slide of the radar screen. By aligning the images with true north and with the ship's global positioning system position, we were able to redraw the coastline in a more realistic location. Although the charted position of the mouth of the bay agreed well with the radar images, the rest of the coast position was rotated counterclockwise as seen in figure 1. Some embayed coastline areas
SARAH E. MAY and CHARLES E. MCCLENNEN Department of Geology Colgate University Hamilton, New York 13346
EUGENE W. DOMACK Department of Geology Hamilton College Clinton, New York 13323
During RIV Polar Duke cruise 90-7 into Andvord Bay, Antarctica (to continue sediment sampling as well as collect seismic and bathymetric data), we noted significant discrepancies in the location of the charted coastline. Global positioning system ship positions, while on station roughly equidistant from each shore near the heads of the bay, repeatedly plotted the ship's position to be on land east of Lester Cove and north of the charted coast. In general, the inner end of the charted position of the bay needs to be pivoted to the northeast by more than 2 kilometers. We used two photographs of the ship's Furuno radar image monitor to plot the position of the shore and glaciers relative to the global positioning system monitor, which simultaneously provided the ship's position. A print of the radar image en128
Figure 1. Charted position of Andvord Bay and the global positioning system radar observed location indicated by the dot shading along the shoreline. Arrows show the general direction of repositioning for Andvord Bay. ANTARCTIC JOURNAL
64°45'
41
62°40'
0
62030'
0^
ANDVORD BAY 400 VO
100 ^x
01,
000
",^ ^\Jl
Deville
Glacier
64°50
64°50' -400 goo
Arao Glacier
0 01
-O ..t,... 0
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:.T.c0oy ?:.
*\
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Nautical Miles 1
2 3
I I I
64°55'
I
1 2 3 4 5 Kilometers
62°40' 162050'
.7/ I
64055'
62030' 62°20']
Figure 2. Bathymetry of Andvord Bay in the revised location. are uncertain in Andvord Bay because they might have been obscured by radar shadows from the ship's position, deep bays, and mountainous landforms. These areas are dashed following the shape of the original charted coastline. We also consulted Landsat images to provide further information on coastline positioning, but the mountain shadows that appear on the images, due to the low sun angle, obscure the northern coast leaving only the southern coastlines relatively clear and identifiable. We plotted the bathymetric data from cruise 90-7 using GI'S latitude and longitude within the repositioned coastline. Bathymetric data from the RIV Polar Duke cruise 88-3 (Domack and Williams 1990) and previously published depths from the navigational chart (Defense Mapping Agency number 29122) were
1991 REVIEW
transposed to fit within the newer coastal position to guide the contouring of bathymetry illustrated in figure 2. This study was supported by National Science Foundation grant DPP 89-15977 to Eugene W. Domack and Charles E. McClennen.
Reference
Domack, E.W., and C.R. Williams. 1990. Fine-structure and suspended transport in three Antarctic fjords. In Contributions to Antarctic Research 1. (Antarctic Research Series, Vol. 50.) Washington, D.C.: American Geophysical Union.
129
Substantial position correction to the Andvord Bay coastline and bathymetry using global positioning system and radar imaging
netic-susceptibility-sensor process when combined with the depositional patterns provide a powerful tool for antarctic paleoclimatic analysis. This preliminary study was supported by National Science Foundation grant DPP 89-15977 to Eugene W. Domack and Charles E. McClennen.
References Andrews, J.T., and A.E. Jennings. 1987 Influence of sediment source and type on the magnetic susceptibility of fjord and shelf deposits, Baffin Island and Baffin Bay, N.W.T. Canadian Journal of Earth Sciences, 24, 1386-1401. Barrett, P.J., A.R. Pyre, and B.L Ward. 1983. Modern sedimentation in McMurdo Sound, Antarctica. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic earth science. Canberra: Australian Academy of Science, Canberra. Domack, E.W., L.A. Burkley, and C.R. Williams. 1989. Character of modern glacial marine sediments: Antarctic Peninsula and South Shetland Islands. Antarctic Journal of the U.S., 24(5), 113-115. Harris, J. S., and E. A. Fleming. 1979. Geologic Map Series BAS500G, Sheet 3, Edition 1. Loubet Coast: British Antarctic Survey.
larged over 10 times, using a Savin 7220 copier, was similar in outline to the projection of a 35-millimeter slide of the radar screen. By aligning the images with true north and with the ship's global positioning system position, we were able to redraw the coastline in a more realistic location. Although the charted position of the mouth of the bay agreed well with the radar images, the rest of the coast position was rotated counterclockwise as seen in figure 1. Some embayed coastline areas
SARAH E. MAY and CHARLES E. MCCLENNEN Department of Geology Colgate University Hamilton, New York 13346
EUGENE W. DOMACK Department of Geology Hamilton College Clinton, New York 13323
During RIV Polar Duke cruise 90-7 into Andvord Bay, Antarctica (to continue sediment sampling as well as collect seismic and bathymetric data), we noted significant discrepancies in the location of the charted coastline. Global positioning system ship positions, while on station roughly equidistant from each shore near the heads of the bay, repeatedly plotted the ship's position to be on land east of Lester Cove and north of the charted coast. In general, the inner end of the charted position of the bay needs to be pivoted to the northeast by more than 2 kilometers. We used two photographs of the ship's Furuno radar image monitor to plot the position of the shore and glaciers relative to the global positioning system monitor, which simultaneously provided the ship's position. A print of the radar image en128
Figure 1. Charted position of Andvord Bay and the global positioning system radar observed location indicated by the dot shading along the shoreline. Arrows show the general direction of repositioning for Andvord Bay. ANTARCTIC JOURNAL
64°45'
41
62°40'
0
62030'
0^
ANDVORD BAY 400 VO
100 ^x
01,
000
",^ ^\Jl
Deville
Glacier
64°50
64°50' -400 goo
Arao Glacier
0 01
-O ..t,... 0
a.
:.T.c0oy ?:.
*\
cc,.
Nautical Miles 1
2 3
I I I
64°55'
I
1 2 3 4 5 Kilometers
62°40' 162050'
.7/ I
64055'
62030' 62°20']
Figure 2. Bathymetry of Andvord Bay in the revised location. are uncertain in Andvord Bay because they might have been obscured by radar shadows from the ship's position, deep bays, and mountainous landforms. These areas are dashed following the shape of the original charted coastline. We also consulted Landsat images to provide further information on coastline positioning, but the mountain shadows that appear on the images, due to the low sun angle, obscure the northern coast leaving only the southern coastlines relatively clear and identifiable. We plotted the bathymetric data from cruise 90-7 using GI'S latitude and longitude within the repositioned coastline. Bathymetric data from the RIV Polar Duke cruise 88-3 (Domack and Williams 1990) and previously published depths from the navigational chart (Defense Mapping Agency number 29122) were
1991 REVIEW
transposed to fit within the newer coastal position to guide the contouring of bathymetry illustrated in figure 2. This study was supported by National Science Foundation grant DPP 89-15977 to Eugene W. Domack and Charles E. McClennen.
Reference
Domack, E.W., and C.R. Williams. 1990. Fine-structure and suspended transport in three Antarctic fjords. In Contributions to Antarctic Research 1. (Antarctic Research Series, Vol. 50.) Washington, D.C.: American Geophysical Union.
129
